1. Field of the Invention
The present invention relates to an automatic control system for controlling the output power of a power plant which operates with hydraulic turbines or steam turbines, and more particularly to an automatic control system categorized as an electrical governor or automatic load regulator (ALR) which automatically controls the output power from a turbine generator.
2. Description of the Prior Art
Generally, power plants of various types operate to control the output power in several manners. In the case of a steam turbine power plant, output power control is implemented either by the manual control system in which the operator manipulates a governor motor, for example, while watching the output power meter or by the automatic control system in which an electro-hydraulic governor, for example, operates to control the output power toward a preset target output power level. Application of the latter system has the premise that the power plant is connected to a power system which is incomparably larger in capacity than the plant.
It has been the convention of a power generating plant, which is instructed by the central load dispatching office to increase or decrease the output, to control the facility in either manual or automatic manner by aiming at the intended final output level. However, in case a power plant has a capacity which is comparable with that of a connected power system, an increase of power generation in anticipation of increasing system load will result in a rising power system frequency unless the system load actually increases as expected. Conversely, a decrease of power generation by simply following a requested target output level will result in a fall in the power system frequency unless the system load decreases as anticipated. These are inherent characteristics of electricity in which generation and consumption take place simultaneously.
An example of automatic load regulators is disclosed in "Standard Specifications for Automatic Load Regulators", pp. 47-48, published on Dec. 5, 1984, by Kansai Electric Power Co., Inc.
It has not been possible, without the presence of the above-mentioned premise, for conventional electro-hydraulic governors and automatic load regulators to control the output power in compliance with the command from the central load dispatching office and varying load conditions while minimizing the variation in the power system frequency, and on the other hand the manual control system has required an enormous operator proficiency and manpower.
Although it is possible to automatically control the power generation together with an automatic frequency control (AFC) system with the intention of balancing the output power and system frequency, such AFC systems are not only complicated, but also quite expensive, therefore these apparatus impose a rise in the initial construction cost.